1. Field
The present invention relates to a power management unit and a system LSI having the power management unit.
2. Description of Related Art
A next-generation LSI has CPU cores (hereinafter simply referred to as CPUs) and logic circuit blocks, each of which belong to different power domains. Separation of the inside of the LSI into power domains makes it possible to reduce the influence of power noise caused by the operating state of a CPU or logic circuit block belonging to one power domain on a CPU or logic circuit block belonging to another power domain.
Recently, reduction of electric power consumption has become an important issue for the next-generation LSI.
In Japanese Patent Laid-Open No. JP-A-7-325647 and ISSCC 2007 Report “Complete Projection of IBM Next-Generation Processor POWER6”, a system of controlling power supply voltages of different power domains independently while controlling clock frequencies independently in accordance with operating states of CPUs or logic circuit blocks belonging to the different power domains is described.
Particularly when a CPU is made to execute a specific process or when a specific logic circuit block is to be operated, the required operating clock frequency and power supply voltage can be estimated in advance. Therefore, when the power supply voltage of the CPU or logic circuit block which will execute the specific process is increased to a required level before the start of execution of the specific process and then the operating clock frequency is increased to a required level, electric power consumption during inexecution of the specific process can be reduced.
As described above, the next-generation LSI has an internal or external power management unit that controls power supply voltages and operating clock frequencies of power domains independently to reduce electric power consumption for the entire LSI.